This invention relates to a method and means for breaking up free-standing boulders, and more particularly, to improvements therein.
In open pit mines, charges of explosive are used to break out in-situ formations of ore breaking rock. The resultant debris is fed into crushers, and eventually processed to remove the desirable ore. A normal consequence of the primary explosion blasting is a distribution of fragment sizes ranging from small rocks to very large boulders. Boulders weighing several tens of tons are typical of the upper sizes obtained. These large boulders are often too large to be moved by vehicles or to fit into the rock crushing apparatus. It is necessary therefore, to break them into smaller fragments. Several schemes are conventionally employed for this purpose. Most commonly a drill rig such as a jackhammer is brought to the boulder and used to drill a bore hole. Explosive is placed in the hole. The crew and drill rig are removed, and the charge is remotely fired. From an energy point of view, this is an efficient process. From a point of view of labor, cost and safety, however, it is very poor. It is often both difficult and unsafe to approach the boulder with personnel and drill rig. It might for example, be surrounded by other boulders or be supported in an unstable manner, such that a small perturbation will make it move suddenly. Because the explosive charges are buried in the rock, the expansion of hot detonation products is very effective in accelerating fragments or rock and propelling them for large distances. This means that equipment and personnel must be removed for large distances before firing, resulting in a very inefficient use of personnel and equipment.
Mud capping is another technique employed. Here, no drill is required. Explosive is placed on the outside of the boulder and tamped with earth or mud. There are also explosive rock breakers which act similarly. These devices are all quite inefficient in the use of explosive. They create a high intensity blast wave. High velocity fragments are still a problem. Also, personnel must still approach and mount the boulder in order to emplace the charges.
Still another technique in fracturing boulders is the use of a large metal ball or swing ball hanging from a crane arm. The crane arm is moved in a manner so that the ball impacts the boulder and fractures it. This technique is often used in quarries, where the boulders are not too large and access to them is straightforward. In a large open pit operation however, the crane cannot always get close enough to the boulders to perform its function.
In quarries, and along mountainous highways, railways, or other thoroughfares, particularly those cut through rock, there are often places where overhanging or loose boulders pose a safety problem. To reach them, in order to employ the above rock breaking schemes is extremely hazardous.